The present invention relates to a semiconductor device having a substantially planar surface and particularly to such a semiconductor device which includes at least one region of polycrystalline silicon on a body of semiconductor material.
In many semiconductor devices, particularly integrated circuit devices, it is desirable that the device have a planar surface over which extends the metallization forming contacts to portions of the device and interconnections between the contacts. This planar surface is desirable so that the metallization does not have to extend over edges which can cause breaks in the metallization. Also, it is easier to define a metallization pattern which is substantially planar.
This problem of providing a planar surface is most apparent in silicon-on-sapphire (SOS semiconductor devices which include a plurality of individual bodies or islands of semiconductor material in spaced relation on a substrate of insulating material, such as sapphire. The spaced bodies of the semiconductor material form ridges over which the metallization must be extended. However, various techniques have been developed to fill in the spaces between the spaced bodies of the semiconductor material with an insulating material so as to provide a planar surface over which the semiconductor surface can extend.
A type of semiconductor device often used in integrated circuit devices and particularly SOS integrated circuit devices is the MOS transistor which includes a gate over the semiconductor material body. One type of gate used is made of polycrystalline silicon which is relatively thick and thus provides a ridge over which metallization must extend. Therefore it would be desirable to have such a semiconductor device which includes a polycrystalline silicon gate with a substantially planar surface over which the metallization can extend.